Senior Labour MPs opposed to Jeremy Corbyn’s leadership have been meeting with the Liberal Democrats in secret talks about setting up a “centrist” pro-Brussels party, sources have claimed.

The Labour leader’s caution over blaming Russia for the Salisbury poisoning was a “watershed moment” that “has caused a number of people to question why we are in this party”, a former member of the Shadow Cabinet toldThe Times.

Hoping to launch a new party in Spring 2019 after Brexit, sources present at the meetings said ‘Start Again’ has emerged as its working title out of a range of possible names, including Back Together, the Democrats, and Regain.

Politicians involved in the talks include past Labour leadership candidate Chuka Umunna, former shadow chancellor Chris Leslie, and Anna Soubry, the arch-globalist Tory MP who claimed it was a “myth” that mass migration put pressure on public services because migrants are “fit young men”.

Hailed by the far-left New Statesman as “the Tory who loves immigration”, Soubry last year said she hoped that MPs would “get on with” creating a new party that could represent “the voice of a moderate, sensible, forward-thinking, visionary middle way, with open minds — actually things which I’ve believed in all my life”.

Labour MP for Wirral South Alison McGovern — who last year as chairman of the Speaker’s Advisory Committee on Works of Art commissioned works featuring ethnic minority individuals to replace artwork in Parliament reflecting the “values and interests” of pre-diversity Britain — is also among figures The Times reports have been meeting each Wednesday to discuss tactics.

According to one individual present at a number of the cross-party meetings, Umunna had talked up the combined membership of pro-EU campaigners in Britain under the same roof as a mighty force.

The source said: “I have heard him on three occasions, in groups of 10 people or more, mention the fact that if you put together the memberships of the pro-European movements you would have something bigger than the Labour Party.”

But on Friday night, Umunna denied plotting to start a new party, according to The Times, which said the former Shadow Business Secretary also denied berating Liberal Democrat leader Vince Cable for having “jumped the gun” in revealing his party could join forces with Labour MPs.